Hi, gae just came out w/ high replication datastore. The bad side effect is that the data you insert into the datastore will not immediately become consistent until after a few seconds in most cases called eventual consistency. If you want to be able to query consistent data, then according to the doc you have to insert the data w/ a parent key and query using the key as ancestor.
1) I understand the reason for eventual consistency i.e. because the backend has to copy the data to all the database nodes to achieve high replication hence the delay of consistency. But why is it if I insert an entity w/ a parent key, then all of a sudden this problem of eventual consistency goes away? The doc ( http://code.google.com/appengine/docs/java/datastore/hr/overview.html) doesn't explain. How does the parentKey (ancestory) solves the problem? 2) Let's say I have a table/entity called "socialsecurity" and column/property is called "number". I chose to have high replication datastore because it's mission critical. The objective is to insert UNIQUE value into "number" property of the "socialsecurity" entity. The problem is after I insert a value ABC, the datastore is not guaranteed to be consistent, so if I do a look up to see if the next value (also ABC) is already in the datastore I may get a false even though ABC is already in the datastore but just not consistent yet. So according to the doc, I should insert the entity w/ some parentKey then query w/ the parentKey as the ancestor? how does it affect the read performance? since I don't understand how ancestor key help w/ eventual consistency I couldn't even speculate on the performance impact. Any db guru can shed some light? -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
